Sandu Liviu Catalin Sandu Liviu Catalin - 3 months ago 33
C Question

LuaJit FFI Return string from C function to Lua?

Say I have this C function:

__declspec(dllexport) const char* GetStr()
{
static char buff[32]

// Fill the buffer with some string here

return buff;
}


And this simple Lua module:

local mymodule = {}

local ffi = require("ffi")

ffi.cdef[[
const char* GetStr();
]]

function mymodule.get_str()
return ffi.C.GetStr()
end

return mymodule


How can I get the returned string from the C function as a Lua string here:

local mymodule = require "mymodule"

print(mymodule.get_str())

Answer

The ffi.string function apparently does the conversion you are looking for.

function mymodule.get_str()
    local c_str = ffi.C.GetStr()
    return ffi.string(c_str)
end

If you are getting a crash, then make sure that your C string is null terminated and, in your case, has at most 31 characterss (so as to not overflow its buffer).

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